<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  
</body>
<script>
  let value = new Set();

  value.add('11')
  console.log(value)
  //如果没有他自己写一个
  _Set = (function () {
      function Set() {
          this.set = Object.create(null);
      }

      Set.prototype.has = function has(key) {
          return this.set[key] === true
      };
      Set.prototype.add = function add(key) {
          this.set[key] = true;
      };
      Set.prototype.clear = function clear() {
          this.set = Object.create(null);
      };

      return Set;
  }());

  let _value = new _Set();

  _value.add('11')
  console.log(_value)
</script>
</html>